1. Summary of the Invention
This invention relates to a watertight receptacle in which the electrical contacts of the receptacle can not be energized when exposed to human touch and in which the electrical plug withdrawal deenergizes the electrical contacts.
2. Description of the Prior Art
Watertight electric outlet receptacle have been in use at shore side and ship board installations for many years. Essentially, one prime application involves refrigerated containers being transported on land with the refrigeration being powered by the transporter. Once at dock side or in place on board ship, the refrigeration unit receives its power from an electrical installation which quite obviously must be watertight due to the wet environment and the associated corrosive problem. Experience has shown that the electrical receptacles, which are typically 220 and 440 volt installations, must be not only protected from the environment but also must not have exposed electrical contacts which can be accidentally or inadvertently contacted by a human.
While there have been many approaches to the problem, there is still a need in the market place for a device which is extremely simple in construction, uses few parts and is low in cost.
In attempting to achieve a design which would overcome these problems one cannot simply look to the extensive electrical receptacle art relating to, by way of example explosion proof electrical receptacles, since the basic criteria for explosion proof receptacles and waterproof receptacles are basically incompatible. Explosion proof receptacles must provide means for gas, which seeps into the receptacle region in which sparking occurs, to be released from the receptacle in the event of an internal explosion due to the spark. This must be done at a rate which is slow enough for the gas to be cool before hitting the atmosphere and therefore avoiding ignition of ambient gas. A watertight receptacle would preclude gas from being released at a regulated rate since the container would have to be totally sealed, but would not entirely preclude entry of gas to the unit due to the far greater permeability of gas than water. In the event of a spark induced explosion, the restricted travel of the gas would either cause the container to blow apart or else, upon rupturing the seal, cause hot gases to be released with the danger of a major explosion occuring. By way of contrast, the controlled fluid egress-ingress provided in explosion proof receptacles would permit moisture and water to enter the receptacle causing corrosion and destroying the value of the device.
Of even greater consequence than the functional difference between the explosion proof and watertight seals, is the difference between the regions which must be sealed. In the waterproof units corrosion must be prevented with respect to all components whereas in explosion proof units, the restricted flow seal must be limited to a confined region around the spark producing switch. Thus, not only is the mode of sealing different, but all of the critical regions to be sealed are different.
For these reasons, attempts to adapt explosion proof receptacles to waterproof applications have met with little success. Typically a specific design for watertight units is required so that all elements can be totally sealed which goes beyond the mere replacement of waterproof seals for restricted flow gaskets.
Looking to the explosion proof receptacle type of prior art one finds that devices have been known for an extensive period of time which can provide some of the currently desired functions. For example, U.S. Pat. No. 1,947,634 issued in 1934 broadly disclosed the idea of locking a plug to a receptacle and controlling the activation of power through a plunger type lever. In 1935 U.S. Pat. No. 2,015,543 disclosed a safety locking mechanism in which a plug cannot be either inserted or removed from a receptacle unless the power control switch was in the off position. Switch boxes or receptacles which have a plug receiving means and an interlock for enabling an electrical switch to be moved to an ON state only when a plug is received in the plug receiving means are known in the prior art. Such arrangements enable power to be supplied only when a plug is properly inserted in a plug receiving means or receptacle. These prior devices as, for example, evidenced in U.S. Pat. No. 1,934,024 issued 1933, 1,971,990 issued in 1934, 1,731,893 issued in 1929, have not proven to be interchangeable or inter-adaptable and a device of the desired simplicity and safety characteristics has not been developed, not withstanding the extensive period in which there has been a need for a reliable, safe, watertight unit which cannot be activated unless a plug is properly in place. U.S. Pat. Nos. 2,420,865 (1949) and 1,947,634 (1934) are illustrative of the time period under discussion.